Feedback control systems are widely used to control the operation of a wide range of devices with applications ranging from mechanical to electrical. A typical application of a feedback control system (often referred to as a controller) involves manipulating some physical device through the use of a manipulation mechanism, controlled electrically and then taking measurements relating to a physical state/status of the device and then using the measurements for additional information to enhance control of the device.
Precise high-bandwidth control requires a controller that provides suitable stability margins. Conventional compensation techniques (pole/zero cancellation or notch filters) exist for applications where fixed resonances impact the controller design. Conventional compensation techniques do not exist for applications where the resonances shift with position of the mechanical device, time, and/or operating temperature without greatly compromising performance or increase complexity.
One possible solution to the problem of shifting resonance in certain applications is to include a mechanical damping device to the system. The presence of the mechanical damping device will greatly simplify the design of the control system and will permit the use of conventional design techniques. However, the addition of a mechanical damping device to certain precise high-bandwidth systems would greatly complicate the fabrication process even if the addition of the mechanical damping device were possible. For example, in a MEMS device, it is often impossible to integrate a mechanical damping device into the system because the MEMS device is fabricated on a silicon (or a similar substance) substrate.
In MEMS devices, mechanical elements, sensors, actuators, and electronics are integrated on a common silicon substrate through the utilization of micro-fabrication technology. Hence, it can be difficult to include devices such as mechanical dampers. Therefore, it is preferred that solutions to the problem of shifting resonance be electrical and computational solutions in nature.
A need has therefore arisen for a control system that is capable of controlling a mechanical device with a shifting resonance near the operating frequency of the device without the inclusion of a mechanical damping device.